- - AGRICULTURE CORE CURRICULUM - - (CLF6000) Advanced Core Cluster: ORNAMENTAL HORTICULTURE (CLF6450) Unit Title: IRRIGATION AND DRAINAGE ____________________________________________________________________________ (CLF6453) Topic: SPRINKLER IRRIGATION Time Year(s) SYSTEMS 4 hours 3 / 4 ____________________________________________________________________________ Topic Objectives: Upon completion of this lesson, the student will be able to: Learning Outcome #: (H-4) - Identify the advantages and disadvantages of various systems of irrigation used in ornamental horticulture (e.g., sprinkler, bubbler, drip, and so forth). (H-5) - Describe factors which determine water penetration. Special Materials and Equipment: An assortment of sprinkler irrigation pipe, sprinkler heads, fittings and assembly tools; a half-pint each of PVC primer and cement. References: Ball, Vic. (Ed.). (1985). BALL RED BOOK (14th ed.). Reston, VA: Reston Publishing Co. Cotton, Lin. (1985). ALL ABOUT LANDSCAPING. Available from: Ortho Books, P.O. Box 5047, San Ramon, CA 94583. Landphair, H. C., & Klatt, F., Jr. (1979). LANDSCAPE ARCHITECTURE CONSTRUCTION. New York: Elsevier Science Publishing Co. Editors of Sunset Books and Sunset Magazine. (1984). LANDSCAPING ILLUSTRATED. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1989). WATERWISE GARDENING. Menlo Park, CA: Lane Publishing Co. Editors of Sunset Books and Sunset Magazine. (1988). WESTERN GARDEN BOOK. Menlo Park, CA: Lane Publishing Co. Wilson, Scott. (1976). LANDSCAPE CONSTRUCTION. San Luis Obispo, CA: California Polytechnic State University, Vocational Education Productions. Evaluation: Unit Exam ===================================================================== *** INSTRUCTORS PLEASE NOTE *** The detail of this topic presentation goes beyond the scope necessary to meet the requirements of the Core Cluster in this area. It will take longer to teach than indicated above if covered entirely. It is included for local enrichment as appropriate to the class. ===================================================================== TOPIC PRESENTATION: SPRINKLER IRRIGATION SYSTEMS REVIEW: As discussed in (CLF6451) Irrigating Ornamental Plants, landscape plantings are usually irrigated by either sprinkler or drip irrigation. Sprinkler irrigation has been used for the longest time, and is the most widely used method of irrigation. It is the only way to effectively irrigate turf. A. Sprinkler systems essentially create artificial rainfall on ornamental plantings. By the use of different nozzles and sprinkler heads, the rate of precipitation, as well as the duration, can be controlled. 1. Sprinklers can be used to irrigate just about any type of ornamental planting. a. The primary use of sprinklers is for a planted area which requires full, even coverage. The best example of this is turf. b. There is a wide variety of special nozzles to allow sprinkling areas of different sizes and shapes. c. Not all sprinklers "sprinkle": 1) "Bubbler" heads are used as part of sprinkler irrigation systems to flood planter boxes and other plantings in retained areas. 2) Mist nozzles can be used to humidify an area and wet down foliage, if this is desired. 2. Sprinklers have been the mainstay of landscape irrigation for decades. Their use enables the maintenance of landscape plantings under conditions which otherwise could not sustain plant life. There are, however, some shortcomings associated with sprinklers which sometimes make other systems preferable. a. Advantages: 1) Correctly laid out, sprinklers provide full, even coverage of a landscaped area. This is particularly important with turf. 2) Sprinklers can be used in uneven terrain. Level surfaces are not necessary as with flood and furrow irrigation techniques. 3) Sprinkling cools and humidifies the microclimate of the irrigated area. This is preferable for many species of landscape plants. 4) Sprinkling plants cleans off dust, and disrupts some pests such as mites. 5) Buried sprinkler lines are relatively strong and subject to little damage if correctly installed. 6) Sprinklers can be used for frost protection of ornamentals, if necessary. (Refer to (CLF7552) Irrigating for further information on this topic.) b. Disadvantages: 1) Sprinkling an area sometimes places water where it isn't needed such as on pavement, mulched areas, and spaces between plantings. This wastes water. 2) Sprinklers often add water to the soil faster than the soil can absorb it. This leads to runoff, which is a waste of water and erodes soil. 3) When water from sprinklers falls on bare soil, crusting (compaction of the top layer of soil) occurs, and the ability of the soil to exchange air and water is diminished. (Mulches and vegetative cover can prevent this.) 4) Sometimes the moisture and humidity from sprinklers can spread plant diseases such as powdery mildew and fireblight. 5) If a sprinkling system is damaged, finding and unearthing the damaged part(s) can be very difficult. 6) Sprinklers require relatively high water flow and pressure to function correctly. B. In order to minimize runoff and the attendant waste of water and erosion, we must have a firm understanding of how water infiltrates (penetrates) the soil, and how it is held once it enters the soil profile. This is critical knowledge in the effective and water-wise application of sprinkler irrigation systems. 1. The water holding capacity of a soil is most directly related to the soil texture. a. A representative loam soil contains approximately 50 percent solid particles (sand, silt, clay, and organic matter), 25 percent air, and 25 percent water: __________________________________ 25 % {| AIR |} {| _________________________________|} {| AVAILABLE WATER |} PORE SPACE 25 % {| - - - - - - - - - - - - - - - - -|} {| UNAVAILABLE WATER |} {| _________________________________|} {|//////////////////////////////////| 50 % {|///////////S O L I D S////////////| {|//////////////////////////////////| {|__________________________________| b. The loam soil represented above is comprised of approximately half solids and half pore spaces (voids). c. The pore spaces are occupied by half air and half water. d. For this loam soil, approximately one half of this water is "available" to plant, and one half unavailable, held tightly by the soil particles. e. When we compare lighter (sandy) soils to this loam we find that the water holding capacity decreases. f. Heavier soils increase in water holding capacity. g. Typically the water holding capacities per foot of soil by textures are: 1) .5 to .75 inches of water per foot of sandy soil, 2) .75 to 1.25 inches of water per foot of loam soil, 3) 1.25 to 2.0 inches of water per foot of clay soil. h. Practically speaking, this means that clay soils require watering less often than sandy soils. i. The amount of soil compaction and the amount of organic matter in the soil will also affect its water holding capacity. 1) Compacted soil holds less water. 2) More organic matter usually means higher water holding capacity, and greater water availability to plants. 2. Water infiltration (water penetration) rates of a soil will vary with several factors. a. Water infiltration is rapid into large continuous pores in the soil; it is reduced by anything that decreases the size or amount of pore space. b. Infiltration rate is rapid in sand, slower in silt, and slowest in clay soils. c. Granular soil structure will increase infiltration rates. d. The greater amount of and the coarser the organic matter in the soil, the faster the water will enter the soil. e. The permeability of and the depth of hardpans, crusts, or other restricting layers will affect the rate of water infiltration. f. Wet soils do not have as high an infiltration rate as dry or moist soils. g. Compaction slows infiltration. h. Warm soils will absorb water faster than cold soils. Frozen soils may not be capable of absorbing water. i. Practically speaking, soils with low infiltration rates must be irrigated using methods which have low precipitation rates. Otherwise, excessive runoff will result. __________________________________________________________ ACTIVITY: 1. Demonstrate to the class the infiltration rate and water holding capacity characteristics of sand, silt and clay. (See details of this demonstration at the end of (CLF 352) "Irrigation Terminology." __________________________________________________________ C. General Principles of Sprinkler Systems: 1. Sprinkler systems operate at relatively high pressures (20-30 psi and higher). 2. Sprinkler systems require relatively high flow rates. An availability of less than 4 or 5 gallons per minute leads to expense and frustration in designing the average residential system. More water flow is needed for larger installations. 3. Sprinkler systems provide uniform areas such as turf with even precipitation rates and full coverage. a. Precipitation rate is the amount of water, in inches, a sprinkler puts on an area in a given amount of time. Other conditions equal, a nozzle with a large orifice will have a higher precipitation rate than a nozzle with a small orifice. b. A sprinkler with half the precipitation rate of another must be allowed to run twice as long to put the same amount of water onto the landscape. c. Overlapping spray patterns are required to achieve a uniform water application. d. To the greatest extent possible, irrigated areas should be overlapped equally to minimize wet and dry spots. These show up most easily on turf, the primary application of sprinkler systems. 4. Accurate design is critical with sprinkler systems. a. Relatively high pressure and flow requirements mean care must be taken not to design irrigation circuits which demand too much of the water supply. If this is the case, the equipment will not work. b. Once the system is in the ground it is time-consuming and expensive to make changes. Irrigation requirements must be accurately assessed at the design stage. 5. Varying the amount of water delivered can be controlled in several ways. For instance, areas requiring less water can have: a. Nozzles with lower precipitation rates. b. Less overlap in spray patterns. c. Less time that the sprinklers are turned on (run time). d. Less frequent irrigations. All of these options result in less TOTAL precipitation. D. As suggested above, the water supply for a sprinkler irrigation system is critical. Some requirements: 1. Adequate Flow: a. If supply lines are narrow or corroded, the gallons per minute that can flow into the system will not be enough to run more than a sprinkler or two at a time. b. Five gallons per minute is about minimum for the average residential system. 2. Adequate Pressure: This is related to flow. Increased flow reduces available pressure. a. 20 pounds per square inch (psi) is about the lowest pressure that can be used for sprinkler systems. b. 30 psi at the operating flow rate is better for average equipment requirements. c. In a system using well water, a pump must be used to pressurize the irrigation system. 3. Adequate Water Quality: If water has high levels of sand, silt, or rust coming through at the source, filters must be used or the irrigation system will not function properly. Valves will jam and nozzles will clog. E. The components of a sprinkler system described below are the basic components of the average sprinkler system. They are listed in the order they would be encountered as water flows through the system. 1. Controller: This unit controls the opening and closing of valves at pre-programmed times. There are a wide variety of controllers on the market now, with varying capabilities. Some of their features: a. Controllers have either built-in or external step-down transformers. They connect to standard 115 volt current and run on 24 volt current. The 24 volt output is safe to run into the field to control valves. b. As few as four or as many as 30 or more valves (or "stations") may be operated by one controller. Usually, only one station is turned on at one time. c. Controllers are either electro-mechanical or solid state in nature. Most modern units are solid state; they offer better dependability, more programming options, and lower cost. d. Some controllers are designed for indoor mounting; more expensive units can withstand outdoor conditions. Special enclosures are available to deter vandals. e. Controllers allow much versatility in irrigating the landscape. 1) Valves can be conveniently turned on and off during early morning hours. a) There is no one working or playing around the landscape who would be inconvenienced by running sprinklers. b) Evaporation rates are low, allowing more water to enter the soil. c) There is less wind in the early morning. This means less water blown away and better spray patterns. 2) Most controllers offer multiple start times. a) This is useful if the soil has a low infiltration rate. b) Heavy soils may require two or three short irrigations (with time in between to allow water to enter the soil) instead of one long one. 3) Most models offer dual programming, which allows lawns and shrubs, with different water requirements, to be irrigated on different schedules. f. Multi-strand wire (24 volt) leads from the controller out to the various remote valves. 2. The point of connection abbreviated "POC" on a blueprint or site plan is where water comes into the landscape area. It may be an existing hose bib or the water meter. 3. The gate valve shuts off the water. a. It situated between the point of connection and the rest of the irrigation system. b. It usually remains wide open, but can be shut down if repairs or additions have to be made to the system. c. Gate valves are not designed to be opened and closed on a regular basis, as a control valve is. 4. A screen and/or filter is installed near the beginning of the system to catch any foreign material coming through the water supply which might otherwise jam the valves or clog up sprinkler nozzles. 5. The backflow prevention device is a legally required part of any irrigation system. a. Its purpose is to protect the public water supply. 1) The backflow preventer keeps water which has entered the irrigation system from backing into the main water supply, in case of a pressure reduction in the supply. 2) This is important because water in the irrigation system can become contaminated with microorganisms, herbicides, insecticides, or fertilizers. b. There are a wide variety of backflow preventers. Two common types are the vacuum breaker and the reduced-pressure (RP) backflow preventer. c. The backflow preventer should be installed behind (downstream of) any valves which control the flow of water out into the landscape. 1) One large unit can be installed at the beginning of the system, or an individual vacuum breaker can accompany each valve at the remote placement of the valve. 2) This latter approach tends to be more common among small installations, with vacuum breakers built into the valve assembly. 3) To function correctly (and to meet code requirements), vacuum breakers must be set 6 to 12 inches above the elevation of the highest sprinkler head or opening on the circuit it protects. 6. A pressure regulator is not required for all systems. a. A pressure regulator adjusts downward the water pressure going into the irrigation system. If pressure is excessive, or varies during operation, sprinkler heads and nozzles will not perform consistently. b. Excessive pressure can cause water to atomize and be thrown by the wind. c. Pressure regulators are available for fixed pressures, or they can be adjustable. Adjustable models are more expensive. 7. Valves open and shut the flow of water from the point of connection to the sprinkler heads. a. There are many types of valves, in sizes from 3/4" on up. b. Manually operated valves, turned on with a key, are giving way to automatically operated valves, actuated by an electro- magnetic solenoid. c. Manual bleed valves allow the manual operation of automatic valves without the use of electricity. This is an important feature which allows a technician to run the irrigation circuit from the field while performing maintenance or troubleshooting. d. Valves are a critical moving part of the system that require proper installation and, over time, servicing or replacement. For this reason valves are not completely buried, but are housed in valve boxes which are accessible from the surface. 8. Irrigation pipe is the backbone of any irrigation system. a. Polyvinyl chloride (PVC) is the primary pipe in use for irrigation systems today. 1) PVC has many advantages: It is light, inert, long- lasting, strong, easy to assemble, and relatively cheap. 2) It comes in sizes 1/2", 3/4", 1", 1 1/4", 1 1/2", 2", 2 1/2", 3", 4", 6" and up. Most residential work is done with pipe under 2" in diameter. Note: These sizes are nominal. Actual inside measurements vary with the grade of pipe. Standard length for PVC pipe is 20 feet. 3) Outside diameters of pipe are always the same so fittings can be standardized. 4) PVC degrades and becomes brittle when exposed to sunlight. Therefore, most of its applications are underground. 5) Schedule pipe is heavier in the small diameters used for most landscaping. It is used for applications requiring more strength. a) Schedule 40 pipe is used for main lines (that part of the system which is under pressure, behind the control valves), and for most standard fittings. b) Schedule 80 is a heavy, gray-colored pipe which is used for applications above grade such as sprinkler risers. 6) Class pipe is lighter in the smaller diameters. It is used for lateral lines (lines past the valves, leading to the sprinkler heads, not usually under pressure). Class 160, and Class 200 pipe are common grade pipes used for landscape work. 7) UV resistant pipe is pipe which resists the degrading effects of ultraviolet light (in sunlight); it is available for situations where trenching is difficult or not desirable. b. Galvanized iron was once the most common material used for sprinkler systems. 1) Presently, it is used only for above-grade situations where extra strength and resistance to light are required. 2) Its many disadvantages include weight, expense, difficulty in plumbing (pipe threading is laborious and time consuming), inflexibility, and rust. 9. PVC fittings all have the same inside diameter for any given size. They are used for a variety of purposes: a. Connecters to join pipe include: 1) ELs (90 degree elbows) 2) TEEs 3) 45 degree elbows 4) Couplings 5) Crosspieces b. Adapters are used to join differing sizes and types of pipe. These include: 1) Male and female adapters, for attaching threaded fittings and pipe to those with slip fittings 2) Bushings, for stepping pipe size up or down 3) Reducer TEEs, to provide and outlets from the lateral line to the sprinkler heads c. Special fittings include compression couplings for repairing pipe breaks and preassembled valve manifolds to save assembly time. 10. Sprinkler heads represent the "end of the line" in an irrigation system, and determine how far and in what direction the water goes. There are a wide variety of sprinkler heads on the market to fit just about every irrigation situation. The main types are described below: a. Spray heads are used in small areas, and spray approximately eight to sixteen feet. 1) Spray heads spray water in small droplets, evenly covering the entire area in the spray pattern at the same time. 2) Spray heads have a high water consumption and generally have shorter run times because so much water is going on the ground at one time. 3) Wind can play havoc with spray heads because the water is in small droplets and can be blown out of the spray pattern fairly easily. 4) Spray nozzles come in a variety of types and sizes. Some examples: a) Spray arcs from 15 degrees through 30, 45, 90, 120, 180, 240, 270 and full circle are available, as well as some adjustable models. b) Nozzles are pre-set for certain distances, typically 8, 10, 12 or 15 feet. Turn-down screws can reduce the "throw" of the nozzle. c) Some nozzles, for use in narrow strips, are designed to throw in a rectangular pattern. d) Pressure compensating nozzles are available to equalize the performance of nozzles operating at different elevations in the landscape. e) Low trajectory or flat spray nozzles are designed to avoid the effects of wind or to be used below interfering branches of trees and shrubs. f) Low pressure and low flow nozzles help in situations where little water pressure is available or a low precipitation rate is desired because of soil conditions. b. Stream spray heads are rotating heads that put out less water at one time; they are designed to throw medium distances, from 10 to 30 feet. 1) The narrow streams of water they project resist the wind more effectively than the tiny droplets from a spray nozzle. 2) Because the precipitation rate is lower on these heads, they are ideal for use on slopes where infiltration is critical. 3) Smaller models will spray several streams at one time; larger models throw a longer distance and use one larger stream. 4) Some stream sprays are gear driven, the gears turned by the flow of water through the head. c. Impact heads are "rainbird" type heads that rotate slowly with the impact of a spring-loaded hammer against the stream of water. 1) They are used in large-scale plantings, set from 25 to 40 feet apart. 2) Impact heads are excellent for operating under low pressure and flows. d. The sprinkler heads described above are available in fixed or pop-up models. 1) Fixed heads are mounted above grade. 2) Pop-up heads are installed below grade, and are designed to pop up when the system is pressurized. The sprinkler pops up anywhere from 3" to 24", depending on the head design, and retracts automatically when the valve closes. Pop-ups have several advantages: a) They remain out of sight when not in use. b) They present less of a tripping hazard in the landscape. c) Because they are below grade most of the time, they are less subject to damage from foot or vehicular traffic. e. Bubblers are a special type of nozzle used to allow a high volume of water to spill out onto the soil in all directions. 1) They are used in planter boxes and for other plantings which have some kind of retainer around them to hold the water in. 2) An adjustment screw on top of the bubbler helps control volume of flow. f. Mist nozzles are for special applications where atomized droplets are desired for humidifying an area. 11. Moisture sensors can be placed in the soil and connected to the controller (either by a wire or by radio communication) to indicate when soil moisture levels are high or low. F. While it takes considerable knowledge and experience to design efficient sprinkler systems, the basic principles are: 1. Sprinkler systems are divided up into circuits. a. Each circuit is controlled by one valve. b. Only one circuit is operated at a time. c. Sprinkler heads on each circuit should be rated to use no more than about 75% of the available flow when they are all added together. For example, if the maximum flow available is 12 gallons per minute at 30 psi, and the sprinkler heads being used are rated for 1.5 gpm at 30 psi, no more than six sprinkler heads should be designed into the circuit. 2. Sprinkler heads on a circuit should all be of the same type and have the same purpose. a. If heads are mixed, there is a dilemma in setting the length of time and frequency for running the circuit. b. For instance, spray heads to irrigate an area of groundcover would put too much water on the ground in the time it takes a rotating streamer to adequately water a large section of turf. c. These applications and head types should not be mixed on the same circuit. 3. As elevation changes in the irrigation system, there is a corresponding change in water pressure. a. As elevation goes up from the water supply, there is a loss of 0.433 pounds of pressure for every foot in elevation increase. (This is often expressed as a half-pound loss for every foot higher in elevation.) b. The gain in pressure is the same: 0.433 psi for every foot lower from the source. c. For example, a sprinkler connected to a source with 40 pounds of pressure available at the required flow, would be operating on a little over 35 psi if the sprinkler head was at an elevation 10 feet higher than the source: 40 psi - [10 feet x 0.433 psi change / foot] = 35.67 psi 4. Pressure loss also occurs through friction with the pipe. a. The larger the pipe diameter, the less friction loss there is. b. Higher water velocity through a pipe results in greater pressure loss. In other words, high flow in a small pipe results in pressure loss. c. Total friction loss depends on pipe size and the length of the circuit. Tables can be used to calculate loss. This is usually not a problem on small residential installations if adequate size pipe is used. 5. When using the majority of rotating head sprinkler designs, those with different coverages (for example, those set to cover a full circle as opposed to those set for quarter- or half-circles) have to be placed on different circuits. a. Rotating heads of any one type put water out at the same rate and travel across their arc at the same rate. b. Consequently, a head which is set for a half circle will yield a precipitation rate double that of a head set for a full circle. c. If these were on the same line, the area covered by the full- circle head would dry out well ahead of the area covered by the half-circle head. The full-circle heads should be run twice as long. This can only be done on separate circuits. 6. Sprinkler systems should be designed with head-to-head coverage. a. Sprinkler heads throw most of their water out away from the head, and rely on the next sprinkler over to cover turf near the head itself. b. Overlap is required for even water coverage. G. When installing a sprinkler system, don't cut corners on effort or expense. A properly installed, trouble-free system will save a tremendous amount of labor and time. Although step-by-step description of installation procedures is beyond the scope of this lesson, some helpful points to remember are listed below: 1. Lay out the system according to the plan devised on paper. a. Use wooden stakes to locate the heads. b. Use gypsum to show where lines will run. c. Use string to keep straight lines where you want them, and use arched bender board to mark even curves. d. PVC will flex to some degree so don't be afraid to design slight bends into the pipe layout. This may be necessary to avoid walkways or other structures. 2. If you need a trench, by all means use a trenching machine for this work. Not only will it save labor, but less of the subsoil will be disrupted, and fewer problems with settling will be encountered. Other points: a. Main (pressurized) lines should be buried at least a foot in most residential situations; many codes require 18 inches. b. Lateral lines should be buried about eight inches. c. Use a 1" galvanized pipe to drive a hole under walkways and paved areas. Water pressure can be used to loosen soil, but this creates a mess. 3. During assembly: a. Work from the control valve out to the heads. b. Use a tray to keep all of the tools needed for PVC assembly together. The tools and materials you should have are: 1) A good PVC shear. These are faster and cleaner-cutting than saws. They leave no burrs on the cut. If you are using a saw, have sandpaper on hand to clean off burrs. 2) A tape for measuring pipe lengths. 3) Clean rags for wiping fittings and excess cement. 4) A pair of channel-lock pliers and small pipe wrenches for installing threaded fittings. 5) A supply of teflon tape for threaded fittings. (ALWAYS tape threaded fittings.) 6) Primer for cleaning and softening PVC. 7) PVC cement for welding slip fittings. 8) All of the fittings needed to do the job. c. Some important points on assembling PVC fittings: 1) Make sure fittings and pipe are free of dirt and debris. 2) If required by code, clean and soften pipe with primer. 3) Working quickly, apply a layer of cement to both the pipe end and the inside of the fitting. Make sure coverage is complete. 4) Push pipe into the fitting, turning the pipe about 1/4 turn as you go in to assure a good weld. Push pipe in until it "bottoms out." 5) Hold the weld in place for about 10 seconds. Some fittings have a tendency to push the pipe back out if it is not held in place. 6) Wipe off excess cement from around the fitting. d. When finished with assembling the system, flush out dirt and dust before attaching the heads. e. Allow welded joints to set for about 6 hours before pressure testing the system. 4. Be sure to test the system completely BEFORE refilling the trenches. a. Check for leaks, proper operation of pop-ups, and consistency in the spray pattern. b. Add heads or circuits if necessary. 5. When testing is complete and installation operates satisfactorily, fill in the trenches. a. After backfilling over 3/4 of the trench, flood the trenches to help settle soil. b. After water has drained off, fill in the rest of the trench with the remaining soil. __________________________________________________________ ACTIVITY: 1. Gather an assortment of sprinkler irrigation pipe, sprinkler heads, fittings, and assembly tools. Review the names of the various supplies, and have students practice fitting and taking apart the various system components, without using PVC cement. 2. Demonstrate the fitting of PVC pipe using primer and cement. Do this demonstration outdoors where there is adequate ventilation. __________________________________________________________ H. Even the most carefully installed systems require periodic maintenance. 1. General maintenance should be performed routinely at least once a year, preferably in the spring. a. Check nozzles for even spray patterns. Nozzles clog easily and need cleaning out periodically. b. Flush filters. The frequency of this chore depends on water quality. c. Check pop-ups. Sometimes pop-ups are reluctant to retract and need adjustment or lubrication. d. Change the back-up battery on the controller annually. This will save programming headaches if there is a power disruption. 2. Troubleshooting is necessary when unexpected problems crop up with a system. Some common problems and probable causes: a. A wet spot develops around the lowest elevation head on a circuit. The usual cause of this is a valve which is not closing completely. Check for foreign matter in the valve, and check seals. b. Dry spots develop in a lawn. This indicates a breakdown in the spray pattern. The usual cause is a clogged nozzle or a stuck pop-up that won't pop up. c. The entire circuit or system is too wet or too dry. This may be caused by a bad setting in the controller, perhaps due to a power disruption. Check controller program. 1/6/91 MH/clh #%&C